This invention concerns a new procedure for producing formyl imidazoles of the general formula 
in which R1 means an alkyl group, by catalytic oxidation of hydroxy methyl imidazoles of the general formula 
in which R1 has the meaning given above.
Formyl imidazoles are important intermediate products, for example, for the production of pharmaceutical substances such as diuretics or antihypertensives (WO-A 92/20651). Several procedures have previously been known for producing formyl imidazoles. In CH-A 685496, a procedure is described in which the catalytic oxidation of hydroxy methyl imidazoles to formyl imidazoles is performed in the presence of noble metal catalysts such as platinum bismuth, platinum black, platinum or palladium on activated charcoal with oxygen insufflation.
The task of the invention was therefore to make available an economical improved procedure for producing formyl imidazoles.
In this invention, this task is solved by the procedure defined in claim 1.
In claim 1, hydroxy methyl imidazoles of the general formula 
in which R1 has the meaning given above, are catalytically oxidized in the presence of a noble metal catalyst and a peroxide to formyl imidazoles of the general formula 
in which R1 has the meaning given above.
R1 has the meaning of hydrogen or an alkyl group, and more particularly a straight-chained or ramified alkyl group with 1 to 6 C atoms. Specifically, this may be methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl and its isomers as well as hexyl and its isomers. The preferred meaning R1 is butyl.
Hydroxy methyl imidazoles can be readily produced as starting compounds as specified, for example, in WO-A 92/20651 or in E. F. Godefroi et al., Trav. Chim. Receuil Pays-Bas, 91, 1383 (1972).
Platinum, palladium, rhodium or gold can be used as the noble metal catalyst. The noble metal is appropriately used in combination with metals such as, for example, bismuth, lead, cerium or indium as the second component. The preferred catalysts are platinum/bismuth or platinum/lead.
The noble metal catalyst is used by itself or bound to a vehicle such as, for example, activated charcoal, silicon dioxide, aluminum dioxide, silicon-aluminum dioxide, zirconium oxide or titanium oxide. It is preferably bound to activated charcoal.
Noble metal catalysts bound to activated charcoal can be commercially obtained, for example, from Degussa.
The appropriate percentage of the noble metal bound to a vehicle is between 0.1 and 15% by weight, and preferably between 0.5 and 7% by weight, relative to the vehicle material.
The noble metal catalyst is preferably used in an amount of 0.05 to 1.0 mol % noble metal base relative to hydroxy methyl imidazole, and an amount of 0.1 to 0.4 mol % noble metal base relative to hydroxy methyl imidazole is especially preferred.
Organic or inorganic peroxides are used as peroxides. Hydrogen peroxide, perborates, a percarboxylic acid, tert-butyl hydroperoxide, cumol hydroperoxide, perbenzoic acid, m-chloroperbenzoic acid, monoperphthalic acid or peracetic acid are well suited, for example. Hydrogen peroxide used in a 10% to 30% aqueous solution is particularly suitable.
The catalytic oxidation takes place appropriately in the presence of water, a water-miscible solvent or mixtures thereof, in an alkaline milieu.
Particularly suitable water-miscible solvents are for example, alcohols or carboxylic acids with 1 to 6 C atoms or ketones such as, for example, acetone or methyl ethyl ketone.
Mixtures of water and water-miscible solvents are preferably used. It has proven to be advantageous if the water used is adjusted to be alkaline, by the appropriate addition of an alkali hydroxide, an alkali carbonate or an alkali acetate. Alkali hydroxide is preferably used in the ratio 1:0.05 to 5, and preferably 1:1 to 3, relative to the mol amount used of the hydroxy methyl imidazole of general formula II.
The catalytic oxidation is appropriately performed at a temperature of 20xc2x0 to 120xc2x0 C., preferably at 50xc2x0-80xc2x0 C.
After the standard peroxide dosing time of 2-3 hours, the compound of general formula I can be isolated in the standard manner after a sufficient secondary reaction time.
The product is isolated by appropriate crystallization and filtration. The catalyst used can be used several times with no loss of activity.